1. Field of the Invention
The present invention relates to the manufacture of thermostructural composite material components, in particular web-like components or panels made by densifying a fibrous preform with a matrix through chemical vapor deposition within the pores of the preform.
A thermostructural composite material is understood to designate a material which has the required mechanical properties to form a structural element and which maintains these properties at high temperatures. Typical examples of such materials are carbon-carbon (C-C) composites, made from a fibrous preform densified by a carbon matrix, and ceramic matrix (CMC) composites, made from a refractory fiber preform (carbon or ceramic fibers) densified by a ceramic matrix. In CMCs, the ceramic material most commonly used for the matrix--and the reinforcement fibers too--is silicon carbide.
Processes for chemical vapor deposition of carbon and silicon carbide are well known in the art, and described in documents U.S. Pat. No. 3,895,084 and FR-A-2 401 888, for instance.
The fibrous preform, which constitutes the reinforcement of the composite material, can be made from various fibrous textures, including felts, cloths or layers of parallel oriented fibers. These textures can be arranged in plies that can be interlinked by needling or by implanting threads according to well-known techniques.
In preparation of the densification, the fibrous preform is placed in a shaping tool, usually made of graphite. The tools serve to maintain the fibrous preform in the desired shape, corresponding to the component to be made, and can also be used to compact the preform in order to obtain the required volume ratio of fibers (the fraction of the preform's apparent volume effectively occupied by fibers).
In a first phase, the chemical vapor deposition of the matrix-forming material is carried out to an extent sufficient to consolidate the preform, that is to obtain a sufficient linking of the fibers to allow the preform to retain its shape when handled, without need for the shaping tool. The consolidated preform can thus be removed from the tool, and the chemical vapor deposition process pursued until the required degree of densification is obtained.
2. Prior Art
The manufacture of relatively large web-like components or panels causes problems at the consolidation stage.
Indeed, because of the component's size and relatively small thickness, as well as the need to incorporate a large number of stiffeners, it is necessary to use highly complex graphite shaping tools.
These tools consist of many parts, on the one hand so as to cover the surface of the preform, and thus hold it in shape and provide the required degree of compacting, and on the other to maintain the stiffeners on the web. Indeed, the stiffeners are integrated at the densification stage. The stiffeners are themselves pre-densified--or consolidated--and their bonding to the remainder of the component is achieved by a co-densification, in which the matrix material effectively "glues" the stiffeners onto the panel or web by virtue of the continuity of the matrix at their interfaces with these components.
These tools are long and expensive to make, and their assembly is complex. Also, in the course of densification, these tools receive a deposit of the matrix material used to manufacture the component. Accordingly, the tools must be renovated each time before being re-used. These renovations cannot be repeated too often, as the tool would otherwise suffer dimensional alterations, or even be deteriorated to the point of being unusable. Consequently, the tools are in practice rejected after only a few uses, considerably increasing the costs of the manufactured components.
Finally, during densification, part of the holding tool can mask the preform, despite the provision of perforations on the tool. This masking hinders the access of the infiltration gas into the pores of the preform, and leads to a non-uniform densification.